All I know about the 2004 time travel film Primer is that it's very confusing. That was made clear in an xkcd plot graph that we linked (Primer is at the bottom right). Although the movie covers only five days, there are nine timelines, according to this graph at Unreality magazine (which you can enlarge at the link). Does this clear things up? Link

Never heard of the movie. Is this like that Inception explanation thing (that I didn't read) that made me think Inception was complicated until I sat down and watched it, and then wondered how anybody could be confused by the plotline?

I wouldn't call it 100% timewasting (especially if it was done by one's double while in the period when two versions of that person are in the same timeline oh god I'm a huge geek); it's actually kind of nice to see that someone puzzled it out and found that the whole thing makes sense within the milieu of the film. It could easy have just been mad randomness for the last 20 minutes or so, and it strengthens the film to know it's more rigorous than that.